The present invention relates to polyester fibers having improved dyeability and particularly to threads and fibers of high-molecular, linear polyesters of poly(ethylene terephthalate) and poly(1,4-cyclohexylenedimethylene terephthalate).
The state of the art of preparing and dyeing poly (ethylene terephthalate) and poly(1,4-cyclohexylenedimethylene terephthalate) fibers may be ascertained by reference to U.S Pat. No. 3,988,387; German Published Application No. 2,502,555 and the book of H. Ludewig, "Polyesterfasern", Akademie Publishers Berlin (1975), pp. 95 et seq. and 199 et seq., the disclosures of which are incorporated herein. The production of the poly(ethylene dodecanedioate) useful in the present invention is possible by the esterification and polycondensation of ethylene glycol and dodecanedioic acid in the same way as it is disclosed for polyesters by Korshak and Vinogradova in "Polyesters", page 153 ff (Pergamon Press 1965).
Threads and fibers of high-molecular, linear polyesters, such as poly(ethylene terephthalate) or poly(1,4-cyclohexylenedimethylene terephthalate) have found widespread use for a great variety of textile applications due to their excellent properties.
The great disadvantage inherent in these threads and fibers, however, resides in that difficulties are encountered when dyeing same in a normal dyeing procedure. Therefore, it has been necessary to either dye textile articles from poly(ethylene terephthalate) or poly(1,4-cyclohexylenedimethylene terephthalate) under pressure at temperatures above the boiling point of the dye bath (HT dyeing) or to conduct the dyeing step in the presence of a carrier.
Apart from the increased expenses involved in such processes, the HT dyeing method cannot be utilized, due to the required high temperatures, for example for polyester-wool mixtures or in the piece-dyeing of carpets. Besides, there is an increasing desire for entirely omitting the use of carriers in the dyeing of polyester threads and fibers, for reasons of environmental protection and prevention of wastewater pollution. Therefore, great efforts have been made to develop polyesters, primarily on the basis of terephthalic acid, ethylene glycol, and 1,4-bis(hydroxymethyl)cyclohexane, which can be thoroughly dyed without the use of HT conditions or a carrier.
The customary method resides in incorporating into the polyester chain of poly(ethylene terephthalate) or poly(1,4-cyclohexylenedimethylene terephthalate) other dicarboxylic acids, such as isophthalic acid, adipic acid, azelaic acid, or dodecanedioic acid, or other diols, such as 1,3-propanediol, 1,4-butanediol, neopentyl glycol, or 1,6-hexanediol, whereby the crystalline structure of the polyesters is disturbed and dye absorption is improved. The disadvantage of this method resides in that the incorporation of these concomitant components into poly(ethylene terephthalate) or poly(1,4-cyclohexylenedimethylene terephthalate) also results in an impairment of the excellent mechanical and thermal properties of the basic polymers. These copolyester threads and fibers are, therefore, no longer usable for certain fields of application wherein these properties are required.
Another process resides in incorporating by blending, during the spinning step, poly(butylene terephthalate), which as is known can be dyed without the use of carriers, into poly(ethylene terephthalate), thus producing polyester threads having an improved dye affinity as disclosed in U.S. Pat. No. 3,988,387 and German Published Application No. 2,502,555. However, it is known from the literature (Polymer 17 (12):1044 [1976]) that poly(butylene terephthalate) is rapidly degraded at high temperatures, splitting off butadiene and low-molecular products. High temperatures are inherently reached during the melt spinning of poly(ethylene terephthalate) and especially of poly(1,4-cyclohexylenedimethylene terephthalate), the melting point of which is about 300.degree. C. A thermal degradation of mixed-in poly(butylene terephthalate) can thus lead to a reduction in viscosity of the total mixture and consequently to an impairment of the mechanical and textile properties of the polyester threads.